The present invention relates to a spud system for a dredging vessel with a longitudinal direction, which spud system comprises a spud carrier for mounting a spud therein in a vertical stance and which spud carrier is moveable with respect to the dredging vessel in a longitudinal direction for advancing the dredging vessel.
In general a cutter suction dredger is fitted with a spud carrier that allows the dredger to be pushed forward when the working spud mounted in the spud carrier has penetrated into the bottom.
In circumstances where large external forces are exerted on the dredger due to sea currents, waves, swell or other causes, overloading of the spud and/or the spud carrier cylinder which drives the spud carrier, is prevented by allowing the spud to move and thus give way to the overload.
However in view of production capacity of the cutter suction dredger, it is important that the neutral position of the spud carrier is a) well defined and that, b) after removal of the overload condition, the spud carrier quickly returns to that neutral position.
The neutral position refers to the carrier and the spud wherein the spud takes a vertical stance.
It is known for spud carriers that are held in a vertical position by means of a wire system, that the overload protection can be realized by allowing at least one of the sheaves to move. As a result the spud carrier will rotate and give way to the overload. Simply connecting a gas spring (accumulator) to this wire system prevents overloading to occur but has as a consequence that there is no well-defined fixed position of the spud before and after overload. Such a spud carrier system is known from WO2006130934 wherein an apparatus is disclosed for accommodating a substantially vertical spud of a dredging vessel with a longitudinal direction, comprising a spud carriage which is mounted for limited rotation around a horizontal transverse axis, wherein at least a first and a second spring means is arranged under bias between the vessel and spud in the longitudinal direction for the purpose of absorbing a moment on the spud carriage, which first and second spring means compensate each other in the non-loaded situation of the spud; and—at least one spring means is provided with a spring force limiting means for limiting the tension in said spring element from a determined maximum moment on the spud carriage.
For spud carriers that do not allow the spud to rotate, it is known to allow the cylinder to yield by releasing oil out of the cylinder to give way to the overload. In that case however, resuming the originally required position is either slow or it requires a lot of pump sets, sensors and power. Such a system is described in the March 2006 issue of “Offshore engineer” in an article titled “Sophisticated controller keeps giant dredger on course” which discusses the hydraulic system for the spud carrier positioning system of a giant cutter suction dredger.